Internal combustion engines may include a fuel rail for distributing fuel to one or more fuel injectors. A pressure of the fuel within the fuel rail may be identified from a fuel rail pressure sensor. The fuel injectors may be operated to inject fuel over a fuel injection pulse-width that is selected, based on the pressure of the fuel within the fuel rail as identified by the fuel rail pressure sensor, to obtain a suitable air-fuel ratio for ignition.
The inventors herein have recognized that degradation of the fuel rail pressure sensor, including sensor failure, may cause uncertainty as to the pressure of the fuel within the fuel rail. As such, a deviation in the amount of fuel injected by the fuel injectors may occur as a result of this uncertainty. United States published patent application number 2007251502 attempts to address this issue by determining whether a pressure sensor is in an abnormal operation state. If the pressure sensor is determined to be in an abnormal operation state, then a duty of a pulse width modulation signal for a fuel pump is fixedly maintained at 100%.
However, the inventors herein have recognized a further disadvantage with the above approach. For example, if the fuel pump is continuously operated at a high pressure setting in response to an abnormal pressure sensor as taught by US 2007251502, then minimum pulse width constraints associated with the fuel injectors may cause an air-fuel ratio formed in the combustion chambers of the engine to be overly rich under some conditions. This deviation in the fuel injection amount may cause excessively rich combustion leading to spark plug fouling during attempted start-up of the internal combustion engine, increased levels of combustion products, and reduced engine efficiency.
To address these or other issues, the inventors have provided an engine system and a method which enables starting of the engine system with a higher fuel pressure to obtain better fuel atomization while also enabling subsequent operation of the engine with a lower fuel pressure even if the fuel pressure sensor is in a degraded state. In one embodiment, the method includes adjusting a fuel pressure within a fuel rail to a first value by operating a high pressure fuel pump to provide pressurized fuel to a high pressure regulation device that exceeds a pressure relief setting of the high pressure regulation device. After the fuel pressure within the fuel rail attains the first value, the method further includes initiating delivery of fuel to the internal combustion engine from the fuel rail by successively injecting fuel directly into combustion chambers of the internal combustion engine. After at least a first fuel injection event, the method includes reducing the fuel pressure within the fuel rail from the first value to a second value over subsequent successive fuel injection events by adjusting an operating parameter of the high pressure fuel pump.
In this way, a higher fuel pressure may be initially obtained to provide increased fuel vaporization and a lower fuel pressure may be thereafter obtained to provide reduced variability in the fuel injection amount at lower engine load conditions, such as at engine idle. This reduced variability may serve to decrease the likelihood of spark plug fouling that may otherwise occur during start-up of the internal combustion engine with a degraded fuel rail pressure sensor. Furthermore, by optionally increasing the air-fuel ratio over successive fuel injection events while the fuel rail pressure is decreasing, the likelihood of spark plug fouling may be further reduced in the event of a failed or degraded fuel rail pressure sensor.